Refactor screen/monitor so that gfx::Screen returns monitor object.

ash/system/tray/system_tray.cc

Index: ash/system/tray/system_tray.cc
diff --git a/ash/system/tray/system_tray.cc b/ash/system/tray/system_tray.cc
index 2f39906c66b4ad9c9b562fe21d4890ba6a3f0c06..efc81669a89f67649853ac74b843ee2358cddbed 100644
--- a/ash/system/tray/system_tray.cc
+++ b/ash/system/tray/system_tray.cc
@@ -28,6 +28,7 @@
 #include "ui/base/accessibility/accessible_view_state.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/gfx/canvas.h"
+#include "ui/gfx/monitor.h"
 #include "ui/gfx/screen.h"
 #include "ui/gfx/skia_util.h"
 #include "ui/views/border.h"
@@ -360,7 +361,7 @@ class SystemTrayBubble : public views::BubbleDelegateView {
           kPaddingFromBottomOfScreen);
       return rect;
     }
-    gfx::Rect rect = gfx::Screen::GetPrimaryMonitorBounds();
+    gfx::Rect rect = gfx::Screen::GetPrimaryMonitor()->GetBounds();
     return gfx::Rect(rect.width() - kPaddingFromRightEdgeOfScreen,
                      rect.height() - kPaddingFromBottomOfScreen,
                      0, 0);